1. Field of the Invention
This invention relates to sensors for measuring the location and the width of an impacted object.
2. Background Art
Sensors and sensing systems for active restraints on vehicles generally include accelerometers, speed sensors, piezoelectric sensors, flex tape switches, ribbon switches and the like. Such prior art sensors and systems do not have the capability of determining the width of an object struck by the sensor on the vehicle. The systems also fail to provide a mechanism for determining the location of an impact on the sensor. Ribbon switches or tape switches such as those disclosed in U.S. Pat. Nos. 3,694,600; 5,847,643; or 6,009,970 produce an output indicating that the strip switch or ribbon switch has been contacted but fail to provide any indication as to the width of the area contacted or the location of the area contacted on the elongated switches.
Information regarding the size and location of a collision would be useful for pedestrian protection systems or airbag deployment systems. If a pedestrian is struck by a vehicle, the greatest risk of injury is the risk of injury to the pedestrian. If, on the other hand, a pole, bridge abutment or another vehicle is contacted by a vehicle, the principal risk of injury is to the driver and passengers of the vehicle. In such instances, impact sensors are used to activate interior active restraint systems such as dashboard airbags or side curtains.
There is a need for sensors that can sense the location and size of an object struck by a vehicle. In side or front impacts, the location and width of the impact zone, if sensed, could assist the vehicle""s crash mitigation system to determine what active restraints should be deployed. Information regarding the location, width and severity of an impact can also be used to control the speed of actuation or selection of particular active restraints that would be most appropriate for the protection of vehicle occupants or pedestrians.
There is a need for a simple, inexpensive device for sensing the severity, location, and width of an impact. This information may be integrated with other sensor outputs by a control system to provide an intelligent crash mitigation system.
According to the present invention, a collision protection system is provided that controls a collision protection apparatus such as an inflatable member or the like. A sensor located on an exterior surface of a vehicle is adapted to provide a width output signal that varies in relation to the width of an object contacting the vehicle. A controller is provided for the collision protection apparatus that receives the width output signal from the sensor and compares the width output signal to a threshold value to determine if the width of the object is less than a predetermined width. The controller actuates the pedestrian collision protection apparatus if the object is less than the predetermined width and exerts a force on the sensor between a lower and an upper threshold.
The system described above may include a collision protection apparatus such as an external inflatable member that is deployed between the object, such as a pedestrian, and the vehicle. The collision protection apparatus may also comprise a hood release that shifts the hood of the vehicle to a raised position that permits the hood to absorb forces applied thereto by the object or pedestrian. The collision protection apparatus may also be an interior active safety restraint system that is actuated either with other restraint systems or independently thereof to protect an occupant of the vehicle from injury caused by a pedestrian who is struck by the vehicle.
According to another aspect of the invention, the sensor may be an elongated strip that extends in a generally horizontal direction across an exterior panel of the vehicle such as the bumper or fender. The strip has electrical contacts that are at least partially compressed in the event of an impact. The width output signal of the sensor is related to the portion of the strip that is compressed. The strip may be a tubular member having at least two spaced electrodes that are normally held apart by the tube. The two spaced electrodes are pressed together along a portion of their length in the event of an impact. The two spaced electrodes provide an electrical signal that indicates the portion of the length of the tube that is compressed. The two spaced electrodes may comprise a carbon ink strip and a copper electrode that are held apart by dielectric dots.
The system may also include an interior sensor secured to a vehicle or location recessed from the surface of the vehicle. The interior sensor may generate an impact force signal in the event of an impact of sufficient force to actuate the interior sensor. The controller may receive the impact force signal from the interior sensor and may disable the collision protection apparatus if it determines that the object struck is not a pedestrian. The interior sensor may be disposed in a cavity formed in a structural foam bumper member.
According to another aspect of the invention, an apparatus for determining if a pedestrian is struck by a vehicle is provided. The apparatus comprises an elongated sensor extending across an exterior region of the vehicle. The sensor has at least two spaced electrodes that are supported on a compressible member. The compressible member is locally compressible along a portion of the region of the vehicle across which the sensor extends. The two spaced electrodes provide an electrical signal that varies in proportion to the portion of the compressible member that is compressed. A controller receives the electrical signal and calculates the length of the portion of the compressible member that is compressed. An impact absorbing member is deployed if the length of the portion of the compressible member compressed is less than a threshold length corresponding to the approximate, predetermined width of a pedestrian at the height of the sensor on the vehicle. The system then determines whether the object struck by the vehicle is a pedestrian.
According to other aspects of the invention, the electrical signal provided by the sensor may also vary in response to the location of the portion of the compressible member that is compressed. If so, the controller may determine the location of the portion of the compressible member that was compressed. The impact absorbing member may be an external inflatable member, a hood raising mechanism, or the like.
According to another aspect of the invention, a sensing system is provided for determining the width of an object in the event of an impact force being applied thereto. The sensing system includes a strip having first and second portions that are spaced apart that connect to a conductive electrode attached to the first portion, and a resistive electrode that is attached to the second portion. A voltage source is connected to the resistive electrode to provide a constant current through the resistive electrode. Upon impact, the conductive electrode contacts the resistive electrode and shorts out the portion of the resistive electrode that is contacted by the conductive electrode. This decreases the resistance of the resistive electrode which decreases the voltage developed.
The sensing system may also comprise a resistive electrode formed as a first part that increases in resistivity from right to left and a second part that increases in resistivity from left to right. The first and second parts are positioned adjacent to one another so that the conductive electrode contacts both parts during an impact thereby shorting the first and second parts of the resistive electrode. By comparing the voltages developed in each part, the width and location of the impact may be determined.
According to another aspect of the invention, the resistive electrode may be formed as a plurality of discrete conductive lines that are located in a generally linear array. Each line is connected to one of a series of resistors so that when the conductive electrode contacts one or more of the conductive lines upon impact, the conductive electrode circumvents the resistors corresponding to the conductive lines. This circumvention reduces the resistance of the resistive electrode and decreases the voltage developed.
These and other aspects of the invention will be better understood in view of the attached drawings and the following detailed description of the several embodiments of the invention disclosed.